Frost management

Frost types

Credit: Scott Barr, Fernfield Wines

There are four phases of frost management: prepare before frost season hits, protect vines when an event occurs, assess damage accurately if it happens, and recover with a clear plan of action.

Radiation frosts behave differently to advection frosts so understanding which of the two types has occurred will help determine management options. 

Prepare for the frost season

Passive frost protection aims to reduce frost risk before it occurs. These strategies generally fall into three categories:

• Modify the microclimate around vines to reduce the risk or severity
• Delay the growth stage of vines, and 
• Insure yourself, physically or financially, to mitigate losses.

Modify the microclimate

The most common ways to reduce radiation frost risk are increasing the temperature around vines or reducing the accumulation of cold air around them.

• Vineyard floor management: Keeping the undervine area bare or mown low exposes soil to the sun, helping it store and later release heat overnight. This may also assist with air movement, allowing cold air to move down a slope. See Undervine management for options to keep the undervine area low.
• Adequate soil moisture: Moisture increases soil’s ability to store heat during the day, which then increases the air temperature at night as the heat is released.
• Vineyard design: When planting a new vineyard or redeveloping a block, there are a range of design factors that can reduce frost risk. These are outlined in this AWRI fact sheet.

Delay the growth stage of the vine

The susceptibility of grapevines to frost increases as vines burst and mature, so delaying the progress of vine growth can reduce damage from both radiation and advection frosts.

For example, one study in Pinot Noir found that a vine at the four-leaf stage (E-L 11) will suffer 50% bud loss at -1.1°C, while a vine at budburst can withstand temperatures down to -2.2°C before the same level of damage occurs. Read the full research paper, Freeze dama|ge of Pinot Noir (Vitis vinifera L.) as affected by bud development, INA Bacteria, and a bacterial inhibitor.

Late pruning is a proven method for delaying growth stage. This can be done as part of a standard program by pruning frost-prone areas last or, for a more extended delay, by leaving extra buds and doing a final prune after budburst has begun. This does come with the cost of extra labour and yield can be reduced as a result. In cool-climate regions, delaying budburst can also shorten the growing season, with a risk that grapes don't reach full ripeness.

Read the research article, Late winter pruning delays budburst, improves fruit composition and reduces frost damage in Sangiovese (Australian Journal of Grape and Wine Research).

Insure yourself (physically or financially) 

The final strategy to prepare for a frost is to consider ways to reduce the financial cost to your business. Crop insurance can reduce the financial impact of frost damage but premiums can be expensive. Check insurance cover options before the start of each season and weigh the cost of coverage against the value of potential losses.

An alternative way to insure yourself is to leave ‘insurance canes’. These are spare canes that are not trained to the cordon but are allowed to remain vertical. If frost damages the cordon, the shoots on the insurance canes, which are higher than the cordon, may remain undamaged and be used to replace the cordon. If not required, they can be removed after the risk of frost has passed.

Protect vines during a frost event

Active frost protection techniques (such as frost fans and sprinklers) are used while frost conditions are occurring. To be effective, these methods must be started before temperatures reach damaging levels and continued until conditions have safely passed.

• Active air movement: works by mixing the warmer air from above with the colder air around the vines. During a radiation frost, cold air settles near the ground while warmer air remains higher up. Frost fans and helicopters mix these air layers, increasing the temperature around the vines and reducing frost damage. They can be costly, require a temperature inversion (radiation frost only) and must be started before critical temperatures occur to be successful. Air movement does not reduce advection frost risk because there isn’t a warm air layer above the vineyard to mix with the cold air.
• Water sprinklers: Water freezing on the plant's surface releases heat, keeping the tissue just above the temperature at which frost damage occurs. Unlike air movement, sprinklers can provide some protection during an advection frost. Sprinklers need to run continuously once started so fresh water keeps freezing and releasing heat, and should only be switched off once temperatures have risen above freezing and the ice begins to melt naturally.

Assess frost damage

Strategies for responding to frost vary significantly based on the type and extent of damage. It is critical to wait for the full effects of a frost to display before deciding on a course of action. While vegetative damage usually appears within a few days, inflorescence damage can take a week or more to appear.

Since frost severity depends heavily on terrain, damage is almost always variable across a vineyard. When assessing damage, map out ‘severity zones’ based on factors like elevation, soil moisture and variety or clone. These often explain why one zone is hit harder than another. Where damage differs between zones, different management strategies may be appropriate.

The AWRI fact sheet Assessing damage after a frost event (PDF) provides a method for estimating the yield of a frost-affected block based on the timing of the frost and the percentage of damaged shoots and inflorescences.

Recover and protect next season's production

Credit: Scott Barr, Fernfield Wines

After damage has been assessed and yield loss estimated, an action plan can be developed. This depends on both the degree of loss and timing, growing season length, quality targets and cost of each action.

In many cases, the best approach is no action, such as where frosts are light or early, where damage in a cool-climate growing region means there won’t be time to ripen a new crop, or where the cost of re-pruning might exceed the crop’s value.

In other cases, the best solution may be to re-prune and start again, such as where a moderate frost would have created uneven ripening, or in a cane pruned vineyard where good replacement canes are essential.

The AWRI e-bulletin Managing frost-affected vines, which was distributed after the severe 2024 frosts, provides detailed guidance on selecting the most appropriate management approach for different frost damage scenarios.

Managing frost-affected vines for the rest of the season

Regardless of whether vines have been re-pruned, or whether no action was required, frost-affected vines may benefit from a change in management for the rest of the season.

Agronomic

• For an early frost, nitrogen application at E-L 12 can help the vine recover since it will have used up its original reserves.
• Frost-damaged tissues are more susceptible to Botrytis if wet weather follows the frost.

 Economic

• The cost of inputs should be weighed against the reduced returns for the season.
• A lighter crop may not justify full spend on the usual program, but weak growth or disease pressure following a frost event can reduce next year's returns.
• The decision on how much to limit costs after a frost event depends on the level of damage, timing, time and/or financial limitations of the grower and risk tolerance.